Movement detection unit

ABSTRACT

A movement detection unit includes a movable body, a first sensor, a second sensor, and a signal processor. The movable body performs a movement in a first direction. The first sensor detects a first magnetic field change which is caused by the movement of the movable body and outputs a first signal. The second sensor is provided in the first direction at a location different from a location of the first sensor. The second sensor detects a second magnetic field change which is caused by the movement of the movable body and outputting a second signal. The signal processor includes a signal generating circuit that generates a third signal and a fourth signal on a basis of the first signal. The third signal and the fourth signal have waveforms different from each other.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/387,184, filed Dec. 21, 2016, the entire contents of which areincorporated herein by reference. This application claims the benefit ofJapanese Priority Patent Application JP2015-255642 filed Dec. 28, 2015,the entire contents of which are incorporated herein by reference.

BACKGROUND

The technology relates to a movement detection unit with a magneticdetection device that detects a change in a magnetic field.

Rotation detection units are generally used to detect rotationalmovements of axles and other rotating bodies. An exemplary rotationdetection unit includes a gear wheel having a magnetic body, and amagnetic detection device disposed in non-contact with the gear wheel(e.g., refer to Japanese Unexamined Patent Application Publications Nos.H6-34645 and 2015-111062).

SUMMARY

In recent years, there has been a demand for rotation detection units todetect a speed of a rotation of a gear wheel even at a low speed withhigh precision. When a gear wheel rotates at a low speed, its angle ofrotation per unit time becomes small. Therefore, the larger number ofteeth in a gear wheel may be preferable in order to detect a smallamount of rotation of the gear wheel.

However, the maximum number of teeth provided in a gear wheel may belimited by various factors, including dimensions of the gear wheelitself and machining accuracy of the gear teeth. Moreover, even if manysmall gear teeth are machined accurately in a gear wheel, there arecases where magnetic field changes around the gear teeth are made smalldue to a decrease in dimension of the gear teeth, and magnetic fieldsproduced by adjacent gear teeth interfere with each other. In this case,detection sensitivity of the magnetic detection device may be decreased.

It is desirable to provide a movement detection unit that detects alow-speed movement with high precision.

A movement detection unit according to an embodiment of the technologyincludes a movable body, a first sensor, a second sensor, and a signalprocessor. The movable body performs a movement in a first direction.The first sensor detects a first magnetic field change which is causedby the movement of the movable body and outputs a first signal. Thesecond sensor is provided in the first direction at a location differentfrom a location of the first sensor. The second sensor detects a secondmagnetic field change which is caused by the movement of the movablebody and outputting a second signal. The signal processor includes asignal generating circuit that generates a third signal and a fourthsignal on a basis of the first signal. The third signal and the fourthsignal have waveforms different from each other.

In the movement detection unit according to the embodiment of thetechnology, the signal generating circuit generates, on the basis of thefirst signal, the third signal and the fourth signal having waveformsdifferent from each other. Therefore, pulses at different timings areobtained on the basis of both the comparisons between the second signaland the third signal and between the second signal and the fourthsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an overall configuration of a rotationdetection unit according to a first embodiment of the disclosure.

FIG. 2 is a circuit diagram of a key part of the rotation detection unitillustrated in FIG. 1.

FIG. 3 is an exploded view of a configuration of a stack of each MRdevice illustrated in FIG. 2.

FIG. 4 is a waveform chart illustrating waveforms of signals generatedin the signal processor illustrated in FIG. 1.

FIG. 5A is a first enlarged view of a key part of the rotation detectionunit illustrated in FIG. 1 and illustrates an operation thereof.

FIG. 5B is a second enlarged view of the key part of the rotationdetection unit illustrated in FIG. 1 and illustrates an operationthereof.

FIG. 5C is a third enlarged view of the key part of the rotationdetection unit illustrated in FIG. 1 and illustrates an operationthereof.

FIG. 6 is a waveform chart according to a modification of the rotationdetection unit illustrated in FIG. 1.

FIG. 7 is a circuit diagram illustrating a configuration of a key partof a rotation detection unit according to a second embodiment of thetechnology.

FIG. 8 is a waveform chart illustrating waveforms of signals generatedin the signal processor illustrated in FIG. 7.

FIG. 9 is a circuit diagram of a signal processor according to anothermodification of the first and second embodiments of the technology.

FIG. 10 is a waveform chart illustrating waveforms of signals generatedin the signal processor illustrated in FIG. 9.

FIG. 11 is a circuit diagram of a signal processor in still anothermodification of the first and second embodiment.

DETAILED DESCRIPTION

Some embodiments of the disclosure will be described in detail belowwith reference to the accompanying drawings. The description will begiven in the following order.

1. First embodiment

A rotation detection unit with a signal generating circuit includingadders

2. Modification of first embodiment

A rotation detection unit having an output signal with a duty ratio of0.5

3. Second embodiment

A rotation detection unit with a signal generating circuit includingamplifiers

4. Other modifications

1. First Embodiment [Configuration of Rotation Detection Unit]

A description will be given below of a configuration of a rotationdetection unit according to a first embodiment of the technology, withreference to FIG. 1, FIG. 2, and some other drawings. FIG. 1 is aschematic view of an overall exemplary configuration of the rotationdetection unit. The rotation detection unit may be a so-called geartooth sensor or a so-called gear sensor. The rotation detection unit mayinclude a gear wheel 1 and a main body 2, for example. It is to be notedthat the rotation detection unit may correspond to a “movement detectionunit” in one specific but non-limiting embodiment of the technology.

(Gear Wheel 1)

The gear wheel 1 may be a rotating body that rotates in a directiondenoted by an arrow 1R. The gear wheel 1 may have a disc-shaped memberprovided with a gear teeth part on its circumference. This gear teethpart may include a plurality of projections 1T and a plurality ofdepressions 1U. These projections 1T and depressions 1U may each be madeof a magnetic body and may be alternately disposed at predeterminedintervals (e.g., about 2 mm to 7 mm). The rotational movement of thegear wheel 1 may cause the projections 1T and the depressions 1U to bealternately positioned at a position nearest to a sensor unit 3 in themain body 2. Details of the sensor unit 3 will be described later. As aresult of the rotational movement of the gear wheel 1, a back biasmagnetic field Hbb which serves as an external magnetic field applied tothe main body 2 may change periodically. Details of the back biasmagnetic field Hbb will be described later with reference to FIG. 5A to5C. It is to be noted that the total number of the projections 1T or thetotal number of the depressions 1U in the gear wheel 1 is referred to asthe number of teeth in the gear wheel 1. The gear wheel 1 may correspondto a “movable body” in one specific but non-limiting embodiment of thetechnology.

(Main Body 2)

The main body 2 may include the sensor unit 3, a signal processor 4, anda magnet 5, for example. The sensor unit 3 may include a sensor circuit30, and the signal processor 4 may include a signal generating circuit40. FIG. 2 is a circuit diagram illustrating exemplary configurations ofthe sensor circuit 30 and the signal generating circuit 40. Asillustrated in FIG. 1, the main body 2 may also have a voltage terminalVcc, a grounding terminal GND, and an output terminal Vout. Via thevoltage terminal Vcc, a power voltage may be supplied to the sensorcircuit 30. Via the output terminal Vout, an output of the signalgenerating circuit 40 may be obtained. In FIG. 1, a distance AG betweenthe sensor unit 3 and the top of the adjacent projection 1T may be in arange from about 0.5 mm to about 3 mm both inclusive, for example.

(Sensor Unit 3)

The sensor circuit 30 may have a Wheatstone bridge circuit includingfour magneto-resistive effect (MR) devices, i.e., MR devices 3A to 3D,for example. A first end of the MR device 3A may be coupled to a firstend of the MR device 3B at a node P1; a first end of the MR device 3Cmay be coupled to a first end of the MR device 3D at a node P2; a secondend of the MR device 3A may be coupled to a second end of the MR device3D at a node P3; and a second end of the MR device 3B may be coupled toa second end of the MR device 3C at a node P4. The node P3 may becoupled to the voltage terminal Vcc; the node P4 may be grounded; thenode P1 may be coupled to the signal processor 4 via a wire L1; and thenode P2 may be coupled to the signal processor 4 via a wire L2. Both theMR devices 3A and 3B may correspond to a “first sensor” in one specificbut non-limiting embodiment of the technology, and both the MR devices3C and 3D may correspond to a “second sensor” in one specific butnon-limiting embodiment of the technology. The MR devices 3A and 3B,which may serve as the first sensor, may be disposed at locationsdifferent from those of the MR devices 3C and 3D, which may serve as thesecond sensor, in the rotational direction of the gear wheel 1 denotedby the arrow 1R.

In FIG. 2, arrows denoted by a character “J31” schematically indicatedirections of magnetization of the magnetization fixed layers 31 in therespective MR devices 3A to 3D. Details of the magnetization fixed layer31 will be described later. Specifically, resistances of both the MRdevices 3A and 3C may change in a first direction with a change in theexternal magnetic field, and resistances of both the MR devices 3B and3D may change in a second direction with a change in the externalmagnetic field. Further, the first direction is opposite to the seconddirection. As one example, when the resistances of the MR devices 3A and3C increase in response to the rotation of the gear wheel 1, theresistances of the MR devices 3B and 3D may decrease.

FIG. 3 illustrates an exemplary sensor stack 3S, which is a key part ofeach of the MR devices 3A to 3D. The sensor stacks 3S in the MR devices3A to 3D may have substantially the same structure. As illustrated inFIG. 3, the sensor stack 3S may have a spin-valve structure in which aplurality of functional films, including a magnetic layer, are stacked.More specifically, the sensor stack 3S may include the magnetizationfixed layer 31, an intermediate layer 32, and a magnetization free layer33 in this order. The magnetization fixed layer 31 may havemagnetization J31 fixed in a constant direction. The intermediate layer32 may exhibit no magnetization in a specific direction. Themagnetization free layer 33 may have magnetization J33 changing with achange in a signal magnetic field. FIG. 3 illustrates a state with noexternal magnetic field, or the back bias magnetic field Hbb. In otherwords, FIG. 3 illustrates a no load state. The direction of themagnetization J33 of the magnetization free layer 33 may besubstantially parallel to its easy axis AE33 of magnetization andsubstantially orthogonal to the magnetization J31 of the magnetizationfixed layer 31. As one example, the magnetization J31 of themagnetization fixed layer 31 in each of the MR devices 3A and 3C may befixed in the +Y direction, whereas the magnetization J31 of themagnetization fixed layer 31 in each of the MR devices 3B and 3D may befixed in the −Y direction. Each of the magnetization fixed layer 31, theintermediate layer 32, and the magnetization free layer 33 may haveeither a single-layer structure or a multi-layer structure including aplurality of layers.

The magnetization fixed layer 31 may be made of a ferromagneticmaterial, examples of which may include, but are not limited to, cobalt(Co), a cobalt-iron alloy (CoFe), and a cobalt-iron-boron alloy (CoFeB).An unillustrated antiferromagnetic layer may be so provided on anopposite side of the magnetization fixed layer 31 to the intermediatelayer 32 that the antiferromagnetic layer is adjacent to themagnetization fixed layer 31. This antiferromagnetic layer may be madeof an antiferromagnetic material, examples of which may include, but arenot limited to, a platinum-manganese alloy (PtMn) and aniridium-manganese alloy (IrMn). As one example, the antiferromagneticlayer in the MR device 3A may be in a state where spin magnetic momentsin the +Y and −Y directions completely cancel each other, and may fixthe direction of the magnetization J31 of the adjacent magnetizationfixed layer 31 in the +Y direction.

The intermediate layer 32 may be a non-magnetic tunnel barrier layermade of magnesium oxide (MgO), for example, and may be thin enough toallow a tunnel current based on quantum mechanics to flow therethrough.In this case, thus, the sensor stack 3S may have an magnetic tunneljunction (MTJ) structure, for example. The tunnel barrier layer made ofMgO may be obtained through a process such as a sputtering process usinga target made of MgO, a process of oxidizing a thin film made ofmagnesium (Mg), and a reactive sputtering process in which magnesium(Mg) is subjected to sputtering in an oxygen atmosphere, for example.Instead of MgO, the intermediate layer 32 may be made of an oxide ornitride of aluminum (Al), tantalum (Ta), or hafnium (Hf), for example.The intermediate layer 32 is not limited to the tunnel barrier layer.Alternatively, the intermediate layer 32 may be a non-magneticelectrically-conductive layer. In this case, the sensor stack 3S mayhave a giant magneto resistive effect (GMR) structure, for example.

The magnetization free layer 33 may be a soft ferromagnetic layer andhave the easy axis AE33 of magnetization in the X-axis direction. Themagnetization free layer 33 may be made of a cobalt-iron alloy (CoFe), anickel-iron alloy (NiFe), or a cobalt-iron-boron alloy (CoFeB), forexample.

When a current I10 is supplied to the Wheatstone bridge circuit in thesensor unit 3 configured above from the voltage terminal Vcc, forexample, the current I10 may flow into both the MR devices 3A and 3D viathe node P3. The current I10 may pass through the sensor stacks 3S inthe respective MR devices 3A and 3D and then reach the nodes P1 and P2.Thereafter, the current I10 may flow into the first ends of therespective MR devices 3B and 3C from the nodes P1 and P2 and then passthrough both the MR devices 3B and 3C. Thereafter, the current I10 mayreach the grounding terminal GND via the node P4. The output from thebridge circuit in the sensor unit 3 from the node P1 may be transmittedas a signal A to the signal processor 4 via the wire L1. Likewise, theoutput from the bridge circuit in the sensor unit 3 from the node P2 maybe transmitted as a signal B to the signal processor 4 via the wire L2.

(Signal Processor 4)

The signal generating circuit 40 included in the signal processor 4 maycorrespond to a “signal generating circuit” in one specific butnon-limiting embodiment of the technology. The signal generating circuit40 may include adders 41A and 41B, comparators 42A to 42C, and acombinational circuit 43, for example. The combinational circuit 43 mayinclude an AND gate 43A, an AND gate 43B, and an OR gate 43C. The signalgenerating circuit 40 may further include a node P5 and a node P6. Thewire L1 may be branched into three routes at the node P5, and the wireL2 may be branched into three routes at the node P6. The signalgenerating circuit 40 may further include wires L3 to L8. The node P5may be coupled to the comparator 42A via the wire L3, to the comparator42B via the wire L4, and to the comparator 42C via the wire L5. The nodeP6 may be coupled to the comparator 42A via the wire L6, to thecomparator 42B via the wire L7, and to the comparator 42C via the wireL8. The adder 41A may be disposed on the wire L3 between the node P5 andthe comparator 42A. The adder 41B may be disposed on the wire L4 betweenthe node P5 and the comparator 42B.

The adder 41A may be a logic circuit that adds a predetermined offsetvoltage to the signal A flowing through the wire L3, thereby generatinga signal A1 and transmits the signal A1 to the comparator 42A. Likewise,the adder 41B may be a logic circuit that adds a predetermined offsetvoltage to the signal A flowing through the wire L4, thereby generatinga signal A2 and transmits the signal A2 to the comparator 42B. In thisexample, the adders 41A and 41B may add, to the signal A, offsetvoltages different from each other, thereby generating the signals A1and A2 having different waveforms from each other. FIG. 4 illustrateswaveforms of the signals A1, A, and A2 together with a waveform of thesignal B. In FIG. 4, the vertical axis associated with the signals A1,A, A2, and B represents a magnitude of a voltage V. FIG. 4 alsoillustrates locations of the projections 1T and the depressions 1U inthe gear wheel 1, a location of the MR devices 3A and 3B, and a locationof the MR devices 3C and 3D. The MR devices 3A and 3B may be hereinaftercollectively referred to as the “first sensor”, and the MR devices 3Cand 3D may be hereinafter collectively referred to as the “secondsensor”. In this example, the adder 41A may preferably add the offsetvoltage, to the signal A, in a range in which the waveform of the signalA1 intersects the waveform of the signal B. Likewise, the adder 41B maypreferably add the offset voltage, to the signal A, in a range in whichthe waveform of the signal A2 intersects the waveform of the signal B.

Each of the comparators 42A to 42C may be a logic circuit that compareslogic values (voltages, in this example) of two input signals, andoutputs a new signal based on a magnitude relationship between thevoltages of the input signals. More specifically, the comparator 42A maycompare the signal B with the signal A1 to which the offset voltage hasbeen added and output a signal C1 based on the comparison result.Likewise, the comparator 42B may compare the signal B with the signal A2to which the offset voltage has been added and output a signal C2 basedon the comparison result. The comparator 42C may compare the signal Bwith the signal A to which no offset voltage has been added and output asignal C based on the comparison result. FIG. 4 illustrates waveforms ofthe respective signals C1, C, and C2. In FIG. 4, the voltage of any ofthe signals A1, A, and A2 corresponds to a high level (Hi) when higherthan the voltage of the signal B, and corresponds to a low level (Lo)when lower than the voltage of the signal B.

The signal generating circuit 40 may further include a wire L9, a wireL10, and a wire L11. The wire L9 may extend from the comparator 42A tothe AND gate 43A. The wire L10 may extend from the comparator 42B to theAND gate 43A. The wire L11 may extend from the comparator 42C to the ANDgate 43A. Disposed on the wire L9 may be a node P7 coupled to the ANDgate 43B via a wire L12. Disposed on the wire L10 may be a node P8coupled to the AND gate 43B via a wire L13. Disposed on the wire L11Amay be a node P9 coupled to the AND gate 43B via a wire L14. In thecombinational circuit 43, after the signals C1, C, and C2 are suppliedto both the AND gates 43A and 43B, the outputs of the AND gates 43A and43B may be supplied to the AND gate 43C, thereby causing a signal D tobe output from the output terminal Vout. FIG. 4 illustrates a waveformof the signal D.

(Magnet 5)

The magnet 5 may be positioned on an opposite side of the sensor unit 3to the gear wheel 1. The magnet 5 may apply the back bias magnetic fieldHbb (see FIG. 5A to FIG. 5C described later) in the +Z direction to boththe gear wheel 1 and the sensor unit 3. The sensor unit 3 may detect achange in the back bias magnetic field Hbb using the MR devices 3A to3D. More specifically, the sensor unit 3 may detect a change in an Xcomponent contained in the back bias magnetic field Hbb.

[Operation and Working of Rotation Detection Unit]

The rotation detection unit of the present embodiment may be able todetect a speed of a rotation of the gear wheel 1, using the sensor unit3, the signal processor 4, and the magnet 5 contained in the main body2.

When the gear wheel 1 that has been in the state of FIG. 5A rotates inthe direction denoted by the arrow 1R, for example, the projections 1Tand the depressions 1U in the gear wheel 1 may alternately face the MRdevices 3A to 3D in the sensor unit 3 of the rotation detection unit. Inthis case, when the projection 1T, made of a magnetic body, approachesthe sensor unit 3 as illustrated in FIG. 5B, for example, the magneticflux of the back bias magnetic field Hbb given by the magnet 5positioned behind the sensor unit 3 may concentrate on this projection1T. In this case, the magnetic flux may spread out to an small extent inthe X-axis direction, so that the X component contained in the back biasmagnetic field Hbb becomes relatively small. In contrast, when theprojection 1T is away from the sensor unit 3 and in turn the depression1U approaches the sensor unit 3 as illustrated in FIG. 5C, for example,a part of the magnetic flux of the back bias magnetic field Hbb may bedirected to the projections 1T on both sides of the depression 1U. Inthis case, the magnetic flux may spread out to a large extent in theX-axis direction, so that the X component contained in the back biasmagnetic field Hbb becomes relatively great. With this change in the Xcomponent contained in the back bias magnetic field Hbb, the directionof the magnetization J33 of the magnetization free layer 33 in each ofthe MR devices 3A to 3D may change. This change in the direction of themagnetization J33 may cause resistances of the MR devices 3A to 3D tochange. By making use of these changes in the resistances of the MRdevices 3A to 3D, the rotation detection unit may detect the speed ofthe rotation of the gear wheel 1.

A detailed description will be given below of an operation of detectingthe rotation of the gear wheel 1, with reference to FIG. 4 and someother drawings. In FIG. 4, the character TH denotes a period over whichany of the projections 1T moves from a location nearest to the firstsensor to a location nearest to the second sensor when the gear wheel 1rotates. Likewise, the character TL denotes a period over which any ofthe depressions 1U moves from a location nearsest to the first sensor toa location nearest to the second sensor. FIG. 4 illustrates an examplecase in which the gear wheel 1 rotates in the direction denoted by thearrow 1R, relative to both the first and second sensors. In FIG. 4, thehorizontal axis represents the passage of time, and the passage of timebecomes greater in a rightward direction of the horizontal axis.

As described above, as the projection 1T approaches the sensor unit 3,the magnetic flux of the back bias magnetic field Hbb from the magnet 5may concentrate on the projection 1T more greatly, so that the Xcomponent contained in the back bias magnetic field Hbb decreases. Incontrast, as the depression 1U approaches the sensor unit 3, a part ofthe magnetic flux of the back bias magnetic field Hbb may be directed tothe projections 1T on both sides of the depression 1U, so that the Xcomponent contained in the back bias magnetic field Hbb increases. As aresult, the signal B on the wire L2 may exhibit a curve as indicated bythe character B in FIG. 4. More specifically, within the period TH, thevoltage of the signal B may gradually decrease to the minimum value andthen gradually increase from the minimum value. Further, within theperiod TL, the voltage of the signal B may gradually increase to themaximum value and then gradually decrease from the maximum value. Thesignal A on the wire L1 may exhibit a curve as indicated by thecharacter A in FIG. 4. More specifically, within the period TH, thevoltage of the signal A may gradually increase to the maximum value andthen gradually decrease from the maximum value. Further, within theperiod TL, the voltage of the signal A may gradually decrease to theminimum value and then gradually increase from the minimum value.

The signal A and the signal B may be supplied directly to the comparator42C via the wires L5 and L8, respectively. The comparator 42C having theforegoing configuration may compare the signals A and B and output thesignal C having a pulse waveform based on the comparison result. Morespecifically, over the period TH, the voltage of the signal A may behigher than that of the signal B, in which case the comparator 42C mayoutput the signal C of a high level (Hi). Over the period TL, thevoltage of the signal A may be lower than that of the signal B, in whichcase the comparator 42C may output the signal C of a low level (Lo) (seeFIG. 4).

The signal A may be supplied to the adder 41A via the wire L3 branchedfrom the wire L1 at the node P5. The adder 41A may add the offsetvoltage to the signal A, thereby generating the new signal A1. Thesignal A1 may be supplied to the comparator 42A. The signal B may besupplied to the comparator 42A via the wire L6 branched from the wire L2at the node P6. The comparator 42A may compare the signals A1 and B andoutput the signal C1 having a pulse waveform based on the comparisonresult. Since the offset voltage is added to the signal A1, the pointsat which the waveforms of the signal A1 and B intersect each other maybe different in location from the points at which the waveforms of thesignals A and B intersect each other. More specifically, a period overwhich the voltage of the signal A1 is higher than that of the signal Bmay be longer than the period TH. Further, a period over which thevoltage of the signal A1 is lower than that of the signal B may beshorter than the period TL. Consequently, a period TH1 over which thesignal C1 is at a high level (Hi) may become longer than the period TH,whereas a period TL1 over which the signal C1 is at a low level (Lo) maybecome shorter than the period TL (see FIG. 4).

The signal A may be also supplied to the adder 41B via the wire L4branched from the wire L1 at the node P5. The adder 41B may add, to thesignal A, the offset voltage different from that added to the signal Aby the adder 41A, thereby generating the new signal A2. The signal A2may be supplied to the comparator 42B. In contrast, the signal B may bealso supplied to the comparator 42B via the wire L7 branched from thewire L2 at the node P6. The comparator 42B may compare the signals A2and B and output the signal C2 having a pulse waveform based on thecomparison result. Since the predetermined offset voltage is added tothe signal A2, points at which the waveforms of the signals A2 and Bintersect each other may be different in location from the intersectionpoints of the waveforms of the signals A and B and the intersectionpoints of the waveforms of the signals A1 and B. More specifically, aperiod over which the voltage of the signal A2 is higher than that ofthe signal B may be shorter than the period TH. Further, a period overwhich the voltage of the signal A2 is lower than that of the signal Bmay be longer than the period TL. Consequently, a period TH2 over whichthe signal C2 is at a high level (Hi) may be shorter than the period TH,and a period TL2 over which the signal C2 is at a low level (Lo) may belonger than the period TL (see FIG. 4).

In the signal generating circuit 40, after the signals C1, C, and C2have been generated in the above manner, the combinational circuit 43may generate a signal D to be output via the output terminal Vout. Asillustrated in FIG. 4, the signal D may contain a plurality of pulses(pulses PL1 and PL2) within the period TH.

[Effect of Rotation Detection Unit]

The foregoing configuration enables the rotation detection unit in thepresent embodiment to output the signal D containing the plurality ofpulses when the single projection 1T passes between the first and secondsensors. One reason for this is that, the signal processor 4 generatesthe signals A1 and A2 having different waveforms on the basis of thesignal A, and the comparators 42A and 42B generate the signals C1 and C2having different waveforms, respectively.

If the signal processor does not generate the signals A1 and A2, onlythe signal C containing a single pulse is obtainable when the singleprojection 1T and the single depression 1U pass between the first andsecond sensors. In contrast, the signal D containing the three pulsesPL1 to PL3 is obtainable when the single projection 1T and the singledepression 1U pass between the first and second sensors.

According to the rotation detection unit in the foregoing firstembodiment, the signal processor 4 is provided. This allows the numberof pulses to be greater than the number of pulses obtainable from only arelationship between the signals A and B. This makes it possible todetect an extremely small rotation of the gear wheel 1 with highprecision.

2. Modification of First Embodiment

In the foregoing first embodiment, the signal D illustrated in FIG. 4contains the pulses PL1, PL2, and PL3. Further, the pulses PL1 and PL2are different in width from the pulse PL3. In addition, the intervalfrom the pulse PL1 to the pulse PL2 is also different from the intervalfrom the pulse PL2 to the pulse PL3. This pulse configuration of thesignal D may involve a complicated numerical process in order todetermine a rotation speed and rotation angle of the gear wheel 1.

To address the foregoing matter, for example, it may be preferable toobtain, from the combinational circuit 43 in the signal generatingcircuit 40, a signal D1 in which a plurality of pulses havingsubstantially the same width are provided at substantially equalintervals, for example, as illustrated in FIG. 6. The foregoing signalD1 may be obtained by adjusting the offset voltages to be added to thesignal A by the adders 41A and 41B. As one specific example, anamplitude of the voltages of the signals A and B may be ±1 V. In thiscase, the adder 41A may add an offset voltage V1 of about +1.732 V(=−2×sin 240°=−2×sin 300°) to the signal A when generating the signalA1. Likewise, the adder 41B may add an offset voltage V2 of about −1.732V (=−2×sin 60°=−2×sin 120°) to the signal A when generating the signalA2. By adjusting the offset voltages in this manner, when the waveformof the signal A intersects the waveform of the signal B at points ofabout 0° and 180°, the waveform of the signal A1 may intersect thewaveform of the signal B at points of about 240° and 300°, and thewaveform of the signal A2 may intersect the waveform of the signal B atpoints of about 60° and 120°. As a result, when the single projection 1Tand the single depression 1U pass between the first and second sensors,the combinational circuit 43 may generate the three pulses each having awidth of about 60° at intervals of about 60°.

By outputting, from the signal processor 4, the signal D1 having a dutyratio of about 0.5 in which the plurality of pulses each havingsubstantially the same width are provided at substantially equalintervals as described above, it is possible to easily determine therotation speed and the rotation angle of the gear wheel 1.

3. Second Embodiment [Configuration and Operation of Rotation DetectionUnit]

Next, a description will be given below of a rotation detection unit ina second embodiment of the technology, with reference to FIG. 7. FIG. 7is a circuit diagram illustrating an exemplary configuration of a signalgenerating circuit 40A in the rotation detection unit in the secondembodiment. In the foregoing first embodiment, the signal generatingcircuit 40 includes the adder 41A that generates the new signal A1 andthe adder 41B that generates the new signal A2. In the secondembodiment, however, the signal generating circuit 40A may include anamplifier 44A and an amplifier 44B, instead of the adders 41A and 41B.The amplifier 44A may generate a new signal A3 based on the signal A,whereas the amplifier 44B may generate a new signal A4 based on thesignal A. Furthermore, the signal generating circuit 40A may receive asignal B0 from the sensor unit 3. A phase difference between the signalsA and B0 may be set to any value other than 180°. Except for this, thesignal generating circuit 40A may have substantially the sameconfiguration as that of the signal generating circuit 40. Hereinafter,components that are substantially the same as those in the foregoingfirst embodiment are denoted with identical characters and will not bedescribed where appropriate.

The amplifier 44A may be an amplifier circuit disposed on the wire L3that couples the node P5 to the comparator 42A. The amplifier 44A mayamplify the voltage of the signal A flowing through the wire L3 within apredetermined range, thereby generating the signal A3. The amplifier 44Amay transmit the signal A3 to the comparator 42A. Likewise, theamplifier 44B may be an amplifier circuit disposed on the wire L4 thatcouples the node P5 to the comparator 42B. The amplifier 44B may amplifythe voltage of the signal A flowing through the wire L4 within apredetermined range, thereby generating the signal A4. The amplifier 44Bmay transmit the signal A4 to the comparator 42B. In this example, itmay be preferable that a ratio at which the amplifier 44A amplifies thesignal A be different from that of the amplifier 44B, so that thesignals A3 and A4 have different waveforms from each other. FIG. 8illustrates waveforms of the signals A3, A, and A4 together with awaveform of the signal B0.

The comparator 42A may compare the signal A3 after the amplificationwith the signal B0, and output a signal C3 based on the comparisonresult. Likewise, the comparator 42B may compare the signal A4 after theamplification with the signal B0, and output a signal C4 based on thecomparison result. The comparator 42C may compare the non-amplifiedsignal A with the signal B0, and output a signal C0 based on thecomparison result. FIG. 8 illustrates waveforms of the signals C3, C0,and C4.

The signals C3, C0, and C4 generated in the above manner may be suppliedto both the AND gate 43A and the AND gate 43B in the combinationalcircuit 43. Thereafter, outputs of the AND gates 43A and 43B may besupplied to the OR gate 43C, following which the OR gate 43C may outputa signal D2 from the output terminal Vout. FIG. 8 illustrates a waveformof the signal D2.

[Effect of Rotation Detection Unit]

According to the rotation detection unit in the second embodiment, theamplifier 44A and the amplifier 44B generate the two signals, i.e., thesignal A3 and the signal A4, respectively, based on the signal A andhaving waveforms different from each other. Therefore, the secondembodiment achieves similar effects as those of the foregoing firstembodiment.

4. Other Modifications

The technology has been described above referring to some embodimentsand the modifications thereof. However, the technology is not limitedthereto and may be varied in various ways. As one example, in theembodiments and the modifications thereof, the signal generating circuitgenerates a plurality of new signals from single signal using adders oramplifiers. However, these configurations may be exemplary and notlimitative.

As one alternative example, a signal generating circuit 40B may includea phase shift circuit 45A that generates a new signal A5 based on thesignal A and a phase shift circuit 45B that generates a new signal A6based on the signal A, as illustrated in FIG. 9. The phase shift circuit45A may be a phase control circuit that includes a coil, a capacitor,and other electrical components and be disposed on the wire L3 couplingthe node P5 to the comparator 42A. The phase shift circuit 45A maygenerate the signal A5 by providing a predetermined temporal shift(delay) to the signal A flowing through the wire L3, and then transmitthe signal A5 to the comparator 42A. Likewise, the phase shift circuit45B may be a phase control circuit that includes a coil, a capacitor,and other electrical components and be disposed on the wire L4 couplingthe node P5 to the comparator 42B. The phase shift circuit 45B maygenerate the signal A6 by providing a predetermined temporal shift(delay) to the signal A flowing through the wire L4, and transmit thesignal A6 to the comparator 42B. In this example, the phase shiftcircuits 45A and 45B may delay the signal A by time perods differentfrom each other, thereby generating the signals A5 and A6 havingwaveforms with different phases from each other. FIG. 10 illustrateswaveforms of the signals A5, A, and A6 together with the waveform of thesignal B.

The comparator 42A may compare the signal A5 that has been subjected tothe phase shift with the signal B, and output a signal C5 based on thecomparison result. Likewise, the comparator 42B may compare the signalA6 that has been subjected to the phase shift with the signal B, andoutput a signal C6 based on the comparison result. Likewise, thecomparator 42C may compare the signal A that has been subjected to nophase shift with the signal B, and output the signal C based on thecomparison result. FIG. 10 illustrates waveforms of the signals C5, C,and C6.

Further, in the combinational circuit 43, the signals C5, C0, and C6generated in the above manner may be supplied to both the AND gate 43Aand the AND gate 43B. Thereafter, outputs of the AND gates 43A and 43Bmay be supplied to the OR gate 43C, following which the OR gate 43C mayoutput a signal D3 from an output terminal Vout. FIG. 10 illustrates thewaveform of the signal D3.

In the present example, the signals A5, A, and A6 may intersect thesignal B at points temporally different from each other. This makes itpossible to output the signal D3 containing the plurality of pulses whenthe single projection 1T passes between the first sensor and the secondsensor. Therefore, it is possible to achieve effects similar to those ofthe foregoing embodiments and the modifications thereof.

Moreover, instead of circuits such as the adders, the amplifiers, andthe phase shift circuits, a multiply circuit may be provided in thesignal processor in order to generate a plurality of new signals havingdifferent frequencies from a single signal.

In the foregoing embodiments and the modifications thereof, an analogcircuit is described as an example of the signal processor. However,this circuit configuration may be exemplary and not limitative.Alternatively, the signal processor may be a digital circuit. In thisexample, for example, a digital comparator may be used as a comparator,and a pulse generator may be used instead of the combinational circuit.In this case, an analog signal from a sensor may be converted into adigital signal by a circuit such as an A/D comparator, for example, tobe supplied to the signal processor.

In the foregoing embodiments and the modifications thereof, the signalprocessor generates three new signals (e.g., the signals A, A1, and A2)on the basis of the signal A from the first sensor. However, the numberof new signals generated may be exemplary and not limited to three.Alternatively, the number of new signals may be two, or four or more.

The signal processor may generate a plurality of new signals Bn (B1, B2,. . . Bn) on the basis of only the signal B from the second sensor.Alternatively, the signal processor may generate a plurality of newsignals Am (A1, A2, . . . Am) on the basis of the signal A from thefirst sensor and may also generate the plurality of new signals Bn (B1,B2, . . . Bn) on the basis of the signal B from the second sensor. FIG.11 illustrates a signal generating circuit 40C as a specific examplethereof. As illustrated in FIG. 11, the signal generating circuit 40Cmay further include an adder 41C and an adder 41D. The adder 41C may bedisposed between the node P6 and the comparator 42A and generate a newsignal B1 on the basis of the signal B. The adder 41D may be disposedbetween the node P6 and the comparator 42B and generate a new signal B2on the basis of the signal B. Except for this, the signal generatingcircuit 40C may have a configuration substantially the same as that ofthe signal generating circuit 40.

Moreover, according to the technology, the number of sensors is notlimited to two or four, and may be any number that is two or greater.

In the foregoing embodiments and the modifications thereof, the gearwheel, which serves as the movable body, has a disc-shaped member with acircumference on which projections and depressions are alternatelydisposed. However, this configuration may be exemplary and is notlimitative. As one alternative example, the movable body may have adisc-shaped or circular member with a circumference on which aferromagnetic part is provided. The ferromagnetic part may be providedwith S-pole regions and N-pole regions that are alternately disposed atpredetermined intervals. In the foregoing embodiments and themodifications thereof, a rotation detection unit, which serves as amovement detection unit, includes a rotating body. However, the rotatingbody may be exemplary and is not limitative. Specifically, the movablebody is not limited to the rotating body as described above.Alternatively, for example, the movable body may be a member thatlinearly extends in one direction. The movement detection unit accordingto one embodiment of the technology may detect a movement, of thislinear movable body, in its extending direction.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

It is possible to achieve at least the following configurations from theabove-described example embodiments of the technology.

(1)

A movement detection unit including:

a movable body that performs a movement in a first direction;

a first sensor that detects a first magnetic field change which iscaused by the movement of the movable body and outputs a first signal;

a second sensor provided in the first direction at a location differentfrom a location of the first sensor, the second sensor detecting asecond magnetic field change which is caused by the movement of themovable body and outputting a second signal; and

a signal processor including a signal generating circuit that generatesa third signal and a fourth signal on a basis of the first signal, thethird signal and the fourth signal having waveforms different from eachother.

(2)

The movement detection unit according to (1), wherein

the movable body includes a gear teeth part having a plurality ofprojections and a plurality of depressions that are alternatelydisposed, and

the signal generating circuit further includes a pulse generator thatgenerates a plurality of pulses within a period in which one of theprojections or one of the depressions passes by both the first sensorand the second sensor.

(3)

The movement detection unit according to (1), wherein

the movable body includes a ferromagnetic part having a plurality ofN-pole regions and a plurality of S-pole regions that are alternatelyprovided, and

the signal generating circuit further includes a pulse generator thatgenerates a plurality of pulses within a period in which one of theN-pole regions or one of the S-pole regions passes by both the firstsensor and the second sensor.

(4)

The movement detection unit according to (1), wherein

the signal generating circuit further includes:

-   -   a first comparator that outputs a fifth signal on a basis of a        comparison between the third signal and the second signal;    -   a second comparator that outputs a sixth signal on a basis of a        comparison between the fourth signal and the second signal; and    -   a pulse generator that combines the fifth signal and the sixth        signal and thereby generates a seventh signal containing a        plurality of pulses.        (5)

The movement detection unit according to (4), wherein

the movable body includes a gear teeth part having a plurality ofprojections and a plurality of depressions that are alternatelydisposed, and

the pulse generator generates the plurality of pulses within a period inwhich one of the projections or one of the depressions passes by boththe first sensor and the second sensor.

(6)

The movement detection unit according to (4), wherein

the movable body includes a ferromagnetic part having a plurality ofN-pole regions and a plurality of S-pole regions that are alternatelyprovided, and

the pulse generator generates the plurality of pulses within a period inwhich one of the N-pole regions or one of the S-pole regions passes byboth the first sensor and the second sensor.

(7)

The movement detection unit according to (1), wherein the signalgenerating circuit further generates an eighth signal and a ninth signalon a basis of the second signal, the eighth signal and the ninth signalhaving waveforms different from each other.

(8)

The movement detection unit according to (7), wherein

the signal generating circuit further includes:

-   -   a third comparator that outputs a tenth signal on a basis of a        comparison between the third signal and the eighth signal;    -   a fourth comparator that outputs an eleventh signal on a basis        of a comparison between the fourth signal and the ninth signal;        and    -   a pulse generator that combines the tenth signal and the        eleventh signal and thereby generates a twelfth signal        containing a plurality of pulses.        (9)

The movement detection unit according to any one of (1) to (8), whereinthe signal generating circuit includes an adder that adds an offsetvoltage to the first signal.

(10)

The movement detection unit according to any one of (1) to (8), whereinthe signal generating circuit includes an amplifier that amplifies thefirst signal.

(11)

The movement detection unit according to any one of (1) to (8), whereinthe signal generating circuit includes a phase shift circuit thattemporally shifts the first signal.

Although the technology has been described in terms of exemplaryembodiments, it is not limited thereto. It should be appreciated thatvariations may be made in the described embodiments by persons skilledin the art without departing from the scope of the invention as definedby the following claims. The limitations in the claims are to beinterpreted broadly based on the language employed in the claims and notlimited to examples described in this specification or during theprosecution of the application, and the examples are to be construed asnon-exclusive. For example, in this disclosure, the term “preferably”,“preferred” or the like is non-exclusive and means “preferably”, but notlimited to. The use of the terms first, second, etc. do not denote anyorder or importance, but rather the terms first, second, etc. are usedto distinguish one element from another. The term “substantially” andits variations are defined as being largely but not necessarily whollywhat is specified as understood by one of ordinary skill in the art. Theterm “about” or “approximately” as used herein can allow for a degree ofvariability in a value or range. Moreover, no element or component inthis disclosure is intended to be dedicated to the public regardless ofwhether the element or component is explicitly recited in the followingclaims.

What is claimed is:
 1. A movement detection unit comprising: a movablebody that performs a movement in a first direction; a first sensor thatdetects a first magnetic field change which is caused by the movement ofthe movable body and outputs a first signal; a second sensor thatdetects a second magnetic field change which is caused by the movementof the movable body and outputting a second signal; and a signalprocessor including a signal generating circuit that generates a thirdsignal and a fourth signal based on the first signal, the third signaland the fourth signal having waveforms different from each other, andcompares a voltage of the second signal to the voltages of the first,third, and fourth signals.
 2. The movement detection unit according toclaim 1, wherein the movable body includes a gear teeth part having aplurality of projections and a plurality of depressions that arealternately disposed, and the signal generating circuit includes a pulsegenerator that generates a plurality of pulses within a period in whichone of the projections or one of the depressions passes by both thefirst sensor and the second sensor.
 3. The movement detection unitaccording to claim 1, wherein the movable body includes a ferromagneticpart having a plurality of N-pole regions and a plurality of S-poleregions that are alternately provided, and the signal generating circuitfurther includes a pulse generator that generates a plurality of pulseswithin a period in which one of the N-pole regions or one of the S-poleregions passes by both the first sensor and the second sensor.
 4. Themovement detection unit according to claim 1, wherein the signalgenerating circuit further includes: a first comparator that outputs afifth signal based on the comparison between voltages of the thirdsignal and the second signal; a second comparator that outputs a sixthsignal based on the comparison between voltages of the fourth signal andthe second signal; and a pulse generator that combines the fifth signaland the sixth signal and thereby generates a seventh signal containing aplurality of pulses.
 5. The movement detection unit according to claim4, wherein the movable body includes a gear teeth part having aplurality of projections and a plurality of depressions that arealternately disposed, and the pulse generator generates the plurality ofpulses within a period in which one of the projections or one of thedepressions passes by both the first sensor and the second sensor. 6.The movement detection unit according to claim 4, wherein the movablebody includes a ferromagnetic part having a plurality of N-pole regionsand a plurality of S-pole regions that are alternately provided, and thepulse generator generates the plurality of pulses within a period inwhich one of the N-pole regions or one of the S-pole regions passes byboth the first sensor and the second sensor.
 7. The movement detectionunit according to claim 1, wherein the signal generating circuitincludes an adder that adds an offset voltage to the first signal. 8.The movement detection unit according to claim 1, wherein the signalgenerating circuit includes an amplifier that amplifies the firstsignal.
 9. The movement detection unit according to claim 1, wherein thesignal generating circuit includes a phase shift circuit that temporallyshifts the first signal.
 10. A movement detector comprising: a movablebody that performs a movement in a first direction; a first sensor thatdetects a first magnetic field change which is caused by the movement ofthe movable body and outputs a first signal; a second sensor thatdetects a second magnetic field change which is caused by the movementof the movable body and outputting a second signal; and a signalprocessor including a signal generating circuit that generates a thirdsignal and a fourth signal based on the first signal, the third signaland the fourth signal having waveforms different from each other, thesignal generating circuit including: a first comparator that outputs afifth signal based on a comparison between voltages of the third signaland the second signal; a second comparator that outputs a sixth signalbased on a comparison between voltages of the fourth signal and thesecond signal; and a pulse generator that combines the fifth signal andthe sixth signal and thereby generates a seventh signal containing aplurality of pulses.
 11. The movement detector according to claim 10,wherein the movable body includes a gear teeth part having a pluralityof projections and a plurality of depressions that are alternatelydisposed, and the pulse generator generates the plurality of pulseswithin a period in which one of the projections or one of thedepressions passes by both the first sensor and the second sensor. 12.The movement detector according to claim 10, wherein the movable bodyincludes a ferromagnetic part having a plurality of N-pole regions and aplurality of S-pole regions that are alternately provided, and the pulsegenerator generates the plurality of pulses within a period in which oneof the N-pole regions or one of the S-pole regions passes by both thefirst sensor and the second sensor.
 13. A movement detector comprising:a movable body that performs a movement in a first direction; a firstsensor that detects a first magnetic field change which is caused by themovement of the movable body and outputs a first signal; a second sensorthat detects a second magnetic field change which is caused by themovement of the movable body and outputting a second signal; and asignal processor including a signal generating circuit that generates athird signal and a fourth signal based on the first signal, and aneighth signal and a ninth signal based on the second signal, the thirdsignal and the fourth signal having waveforms different from each other,and the eighth signal and the ninth signal having waveforms differentfrom each other, the signal generating circuit including: a thirdcomparator that outputs a tenth signal based on a comparison betweenvoltages of the third signal and the eighth signal; a fourth comparatorthat outputs an eleventh signal based on a comparison between voltagesof the fourth signal and the ninth signal; and a pulse generator thatcombines the tenth signal and the eleventh signal and thereby generatesa twelfth signal containing a plurality of pulses.
 14. The movementdetector according to claim 13, wherein the movable body includes a gearteeth part having a plurality of projections and a plurality ofdepressions that are alternately disposed, and the pulse generatorgenerates the plurality of pulses within a period in which one of theprojections or one of the depressions passes by both the first sensorand the second sensor.
 15. The movement detector according to claim 13,wherein the movable body includes a ferromagnetic part having aplurality of N-pole regions and a plurality of S-pole regions that arealternately provided, and the pulse generator generates the plurality ofpulses within a period in which one of the N-pole regions or one of theS-pole regions passes by both the first sensor and the second sensor.